1. Field of the Invention
The invention relates to an apparatus, based on the principle of the displacer counter, for measuring quantities of liquid in gasoline pumps of motor vehicle filling stations during a fuelling process.
2. Discussion of the Related Art
For measuring quantities of liquid supplied to gasoline pumps of motor vehicle filling stations, it is generally known and common practice to use displacer counters, such as liquid measuring motors constructed in the manner of a piston slide valve. Such liquid measuring motors have the drawback that the liquid to be measured has to be supplied via a rotary slide valve to periodically and successively separated working chambers and connected, in a further control channel, to the outlet. During said process the liquid changes direction several times. There is also, in many cases, no linear correlation between revolution and throughflow volume. Finally, problems arise with adjustment of the delivery volume through piston stroke movement if high precision is an important factor and the counters, for billing measurements in the filling station business, have to be calibrated and regularly recalibrated under operating conditions.
EP 0 016 928 B1 discloses a throughflow measuring device, which operates as a flow meter and has a cylindrical rotational solid having, on its outer periphery, helical turns which act as flow-past vanes and generate a torque at the rotational solid.
In a throughflow measuring device according to EP 0 069 170 B1, likewise operating as a flow meter, a turbine wheel is used as an impeller wheel, its rotational speed and hence the throughflow of the liquid being measured using the light barrier principle. The electrical signals are supplied to an electronic measuring device and converted into an electrical measured variable. The throughflow measuring device is intended particularly for use as a fuel consumption meter for motor vehicles.
In each of said known throughflow measuring devices, only a single rotational solid is provided in the flow channel. The measuring accuracy and appropriateness for verification of the throughflow measurement of liquid fuels in filling stations therefore depend exclusively on the cross-section of flow along said rotational solid as well as upon the shaping of the helical turns.
A screw spindle arrangement having a plurality of rotary screws which engage one into the other is known from CH-PS 187 466. One of the rotary screws is connected to a counting mechanism for indirect measurement of the throughflow quantity of flowable media, such as liquids, and is provided at one end with a driving gear which, via a speed-transforming gear, drives the pointers of the counting mechanism.
The drawback of said style of construction is that mechanical gear parts have to be used for transmission of the rotary motion with simultaneous speed reduction between the rotary screw and the counting mechanism pointers. A plurality of these mechanical gear parts have to be provided depending on the number of pointers to be set in rotation, and the gear parts have to be sealed off from the liquid to be measured and are also exposed to wear.
From DE 39 42 857 C1 it is known, when using a quite conventional piston-type device for measuring the dispensed volume of fuel, to couple the piston-type measuring device to an optoelectronic pulse generator, whose pulses generated as a function of the measured volume of fuel are fed into a computer head. The drawbacks described initially in connection with fluid measuring motors constructed in the manner of a piston slide valve also apply to this known form of construction.
An apparatus which is appropriate for verification and by means of which the throughflow may be measured and adjusted to a setpoint value is disclosed in U.S. Pat. No. 4,831,866. Measurement is effected by a volumetric displacement chamber. Adjustment is effected by electronic intervention into the pulse processing in such a way that a calibration factor for correcting the pulse number derived from the throughflow measuring device is automatically acquired during a fuelling process and is acquired after specific operating or dispensing intervals which each correspond to a specific volume of liquid.
From DE 28 05 191 A1, a recording device for dispensing goods, in particular liquid motor vehicle fuel, in filling stations is known in which, to simplify billing, two pulse generators are associated with a throughflow measuring device and supply two counting pulse trains to a test circuit which produces a counting signal if they match and an error signal if they do not match. What is involved here, however, is merely a coincidence circuit by means of which double checking may be effected when billing for the dispensed quantity of fuel.